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Top space boffins say that they have discovered signs of ice on a second asteroid, indicating that water may be commonly found throughout the asteroid belt - which would be good news indeed for humanity's future in space, as well as offering an intriguing insight into the remote past of Earth.

It was announced in April that water and organic compounds had been detected on 24 Themis, a 120-mile-wide space rock which circles the Sun betwen the orbits of Mars and Jupiter. Now the same scientists say they have made similar discoveries on 65 Cybele, another hefty space lump of the outer main asteroid belt.

"This discovery suggests that this region of our solar system contains more water ice than anticipated," says Professor Humberto Campins, one of the investigating boffins. "And it supports the theory that asteroids may have hit Earth and brought our planet its water and the building blocks for life to form and evolve here."

Speculation on the origins of Earthly water and life are of great scientific interest, but the presence of large amounts of water ice in the asteroid belt is also a big potential deal for humanity's future as well as its past.

Not only would water be very useful for drinking, washing etc and as an oxygen source for astronauts, it is also a potential source of rocket fuel (or perhaps reaction mass for more advanced interplanetary engines). One of the great limiting factors on human activity in space is the need to haul vast amounts of propellant along on every journey: and, in the case of manned voyages, even more for the trip back.

The USA until recently intended to establish manned bases on the Moon, and a key factor in how much those bases would cost to run was the presence or absence of exploitable water ice on the lunar surface: hence the "moon bombing" LCROSS polar impact probe last year.

President Obama has now said that the US will not return to the Moon, so the question of ice mining there becomes somewhat academic unless and until another nation steps up. However, Obama has also said that US astronauts will venture again beyond low Earth orbit, with the ultimate goal of a landing on Mars: but that a mission to a (near-Earth) asteroid will take place first.

Manned flights to and from the asteroids could potentially reap the same benefits from ice mining as Moon missions and bases would: and do so more easily, as there is no lunar gravity field to lift the resulting propellants out of. (Even relatively far-flung asteroids orbiting beyond Mars, like 24 Themis and 65 Cybele, would be technically easier to visit and return from than the Martian surface.)

The prospect even exists of asteroid ice or chemicals mining paying for itself in the nearish future, via the only real commercial space business in the world today - that of satellites in Earth orbit, used for many purposes and generating huge revenues.

At the moment, despite the huge costs of making and launching a satellite, it must be decommissioned and destroyed once its supply of manoeuvring propellant runs low: there is no option to refuel it. Proof-of-concept missions have shown that there's no technical obstacle to sending up robotic refueller craft, but the costs of lifting payload up through Earth's thick atmosphere and deep gravity well are so vast that the economics of satellite refuelling from the mother planet are dubious.

But asteroid ice, in terms of gravity and energy, is actually above Earth orbit already. Very little push would be necessary to bring it to the thirsty satellites that we rely on for comms, navigation, observation and so on.

It might not just be manned missions and bases among the asteroids and the planets which could benefit from the findings of space ice made this year, then. Down the road the bodies signing the cheques to send the ships out to the Belt might not be government space agencies, but ordinary financiers of the sort who today send up so many satellites, seeking to get more value out of their multibillion dollar hardware in orbit above Earth. Satellites and ships of the future would still no doubt be made down here, but they might very well launch to orbit unfuelled one day, saving hugely on launch costs.

Further down the road, anything at all which can be found among the asteroids might become cheap - not just in orbit but down here on Earth, as it could be dropped down to us with ease. (Presence among the asteroids would also, of course, offer the scope for extremely destructive kinetic space bombings - suggesting that the military would not let itself be left behind in the rush to the Belt.)

Thus it behoves to find out all we can about what's out there among the space boulders. The latest 65 Cybele research by Campins and his colleagues, announced on Friday at a Californian science conference and set to be published in the journal Astronomy and Astrophysics, is very timely. ®